Effect of Particle-Size Distribution on Wall Friction in High-Velocity Gas-Dynamic Apparatuses

The mechanism of the friction of particles of a polydisperse material on the channel wall is considered under the assumption the friction loss of energy is caused by multiple semielastic collisions of the particles against the wall. A model is suggested for calculating energy losses in the design of the nozzles and vortex chambers of jet mills. A parametric study of the model is carried out, and the effect of particle friction on the parameters of the gas–particle flow is evaluated for these apparatuses.     

An investigation of carbon nanotube jet grinding

Since their observation in 1976 and 1991, carbon nanotubes (CNTs) have generated much interest due to their properties and potential applications. CNTs are tubular carbon molecules with remarkable mechanical, electrical, chemical and thermal properties, which make them useful in various applications. Industries producing CNTs via the fluidized bed chemical vapor deposition technique face challenges related to the size of CNT bundles. The two main challenges are agglomeration and agglomerate size distribution control. A solution to these challenges involves the use of jet mills to grind the CNT agglomerates. The goal of this study was to determine whether the nanotubes could be ground with air jets using a commercial jet mill and apply a two-parameter model to describe the grinding process. The present study has indicated that air-jet grinding of CNTs is feasible with a typical commercial jet mill. This paper presents the effect of operational parameters on the arithmetic mean diameter of the ground product. Sonic velocity through the grinding nozzles was required to obtain reasonable grinding rates and relatively narrow particle size distributions. This occurs at high air to solids feedrate ratios. Additionally, a simple attrition model can describe the grinding process in the spiral jet mill.     

Impingement Heat Transfer for a Cluster of Laminar Impinging Jets Issuing from Noncircular Nozzles

Abstract:

Results of numerical simulation of the flow and heat transfer characteristics for a semi-confined cluster of laminar air jets impinging normally on a plane wall are presented. A central jet is surrounded by four equally spaced jets of the same configuration. Both circular and noncircular nozzles are considered. The nozzle footprint is displayed in the static pressure, temperature, and local Nusselt number contours on the impingement surface only for relatively short nozzle-to-surface distances. The heat transfer characteristics and performance of circular and noncircular nozzles are compared. It is observed that the Nusselt number based on property values at the jet temperature is relatively insensitive to the temperature difference between the jet and the impingement surface. Also, the local Nusselt numbers are independent of the thermal boundary condition; i.e., the values are nearly the same for both isothermal and uniform heat flux conditions at the target surface. Finally, Nusselt numbers for a single equivalent jet viz. one with the same area as the five nozzles in the cluster combined, are compared for the case of the circular jet.     

New concept: Low-pressure,wide-angle atomiser

Paper summarises results obtained in feasibility study of a novel pneumatic atomiser for generation of a spray of fine droplets. The new feature is pulsation of supplied air so that it issues in anti-phase from two nozzles acting on the water jet. The pulsation is generated using an integral no-moving-part fluidic oscillator. Tests involved recording by high-speed camera and laser-light scattering measurements of droplet size. Despite the low pressure (<10 kPa) of supplied air, the mean diameter of droplets was small – mere 158 μm – and the spray fan angle full 90 deg.     

两喷嘴对置撞击流径向射流流动特征

对喷嘴间距与喷嘴直径比为0.5～100范围内两喷嘴对置撞击流径向射流的湍流脉动特征、速度分布和扩展率等进行了实验研究和数值模拟。研究结果表明,撞击流径向射流明显较自由射流湍动强烈;从驻点开始径向射流速度逐渐增大到最大值后开始衰减,射流呈现自相似性;随着喷嘴间距增大,撞击流径向射流的扩展率呈现增大的趋势,大约为自由圆射流的1.5～3倍。采用CFD软件对撞击流径向射流的速度分布特征进行了数值模拟,与实验结果相比,两方程湍流模型预报的撞击流径向射流的扩展率明显偏小,雷诺应力模型的预报精度有较大改进。     

行列式刚性陶瓷过滤器脉冲反吹系统中的压力特性

利用高频动态压力传感器测定脉冲反吹系统中各位置的压力特性,研究了反吹压力和喷嘴孔径对压力特性的影响,提出了解决反吹不均匀的设计方案,采用过滤循环实验进行验证. 结果表明,采用相同孔径的喷嘴时,喷吹管内、喷嘴出口及过滤管内的压力特性存在较大差异,各喷嘴的反吹不均匀性随反吹压力升高而增大,反吹强度随喷嘴孔径增大而减小,喷吹管内的静压沿喷吹方向逐渐增大. 沿喷吹方向将喷嘴孔径递减能改善反吹不均匀的状况,喷嘴截面积与喷吹管截面积之比s/S对脉冲反吹均匀性的影响较大,s/S=48%~55%较佳.     

Enhancement of Heat and Mass Transfer with Innovative Impinging Jets

Impinging jets are widely used throughout various industries. The nozzle design used most frequently for jet impingement is the in-line jet. There have been many attempts at altering a jet's flow to increase its transport characteristics. The transport characteristics of two recently developed innovative and practical submerged impinging jets are described. Specifically, the heat and mass transfer characteristics of the Radial Jet Reattachment (RJR) nozzle and Self-Oscillating Jet Impinging Nozzle (SOJIN) are presented and cornoared lo the in-line iet nozzle. Both nozzles orovide high transport Coeficients. The RJR nozzle is for applications where'it is crucial to control the normal force on the imoinaement surface and those aoolications where space above the surface is to be minimized. The SOJIN offers an inexpensive modification to in-line nozzles in order to increase their transport properties. The SOJIN is exceptionally beneficial when standard in-line nozzles are required to work closer to the impingement surfaces than their optimal spacing.     

催化裂化再生器树枝状气体分布器喷嘴的射流特性

在催化裂化装置中再生器底部通常设置有树枝状管式气体分布器,通过分布器上的喷嘴分布气体。但在实际运行过程中喷嘴常出现布气不均和磨损问题,影响其自身的布气性能和使用寿命。为此,在二维床实验装置上针对喷嘴的射流特性进行了实验研究。实验物料为FCC催化剂颗粒,喷嘴出口气速范围为30～70 m·s^-1,喷嘴喷射角度范围为0°～67.5°。实验用摄影观察法测量喷嘴射流的射流长度和附近的流场流态。实验结果表明射流长度随喷嘴气速和喷射角度的增大而变长。射流气体在向上翻转过程中,在树枝状管式气体分布器两分支管之间产生旋转涡流现象,旋转涡流的大小与喷嘴出口气速和安装角度有密切关系。最后基于实验数据,建立了喷嘴射流长度的计算模型。     

An Electrospray Method Using a Multi‐Capillary Nozzle Emitter

A multi‐capillary nozzle emitter consisting of one metal plate with capillary nozzles and a ring type counter electrode was used as a multi‐electrospray atomizer. The number of capillary nozzles, flow rate of the liquid and the interval between the capillary nozzles were changed, and the droplet diameter and the voltage required for a steady cone‐jet mode were measured. For the multi‐capillary nozzle emitter, the interaction between the capillary nozzles is the important factor for obtaining fine droplets of uniform size. These fine droplets are obtained when there is only a small interaction between the capillary nozzles, and the equations obtained from the single capillary nozzle case are also applicable for the multi‐capillary nozzle emitter. When the number of capillary nozzles decreases (a situation which is not good for obtaining a large amount of droplets) or the interval between the capillary nozzles increases, the interaction between the capillary nozzles can be reduced. As the number of capillary nozzles increase, a higher voltage is required to obtain a fine droplet of uniform size.     

Study of gas-liquid jet boundaries in a gas-solid fluidized bed

The boundaries of gas-liquid jets formed during the air-assisted injection of liquids into gas-solid fluidized beds have been investigated using a small and a commercial scale fluidized bed and several injection nozzles. Two independent techniques (a triboelectric probe system and a thermal tracer method) have successfully allowed the characterization of the jet angle, of the jet penetration, and of the overall mapping of the jet cavity.The study demonstrated the effects of the nozzle geometrical configuration, of the air-to-liquid mass ratio fed through the nozzles, and of the scale of the fluidized bed on the jet boundaries.Finally, the experimental results obtained in this work confirmed the accuracy of an empirical correlation for jet penetration available in the literature.     

Enhancement of Heat and Mass Transfer with Innovative Impinging Jets

ABSTRACT

Impinging jets are widely used throughout various industries. The nozzle design used most frequently for jet impingement is the in-line jet. There have been many attempts at altering a jet's flow to increase its transport characteristics. The transport characteristics of two recently developed innovative and practical submerged impinging jets are described. Specifically, the heat and mass transfer characteristics of the Radial Jet Reattachment (RJR) nozzle and Self-Oscillating Jet Impinging Nozzle (SOJIN) are presented and cornoared lo the in-line iet nozzle. Both nozzles orovide high transport Coeficients. The RJR nozzle is for applications where'it is crucial to control the normal force on the imoinaement surface and those aoolications where space above the surface is to be minimized. The SOJIN offers an inexpensive modification to in-line nozzles in order to increase their transport properties. The SOJIN is exceptionally beneficial when standard in-line nozzles are required to work closer to the impingement surfaces than their optimal spacing.     

Influence of electric field interference on double nozzles electrospinning

The low production rate of electrospinning process may limit the industrial use of single needle system. To meet high yield requirement and uniform fibers, a bottom‐up multiple jets electrospinning nozzle was designed, each nozzle can emit 6–18 jets. The influence of electric field interference on jet path, membrane shape, and fiber morphology were investigated. Experiment finds that electrical field strength in the closer part of two nozzles is weakened because of electric field interference when the distance between two nozzles is 30 mm, making the jet hard to emit in this section, and closer part of electrospun fiber webs has fewer fibers. The spinning in far side part of two nozzles is similar to that of single nozzle. While in middle part of one nozzle, the jet path is short, elongation of jets smaller, the formed fibers thicker, solvent evaporation less sufficient. When the distance of two nozzles is increased to 50 mm, influence of electric field interference is weaker, the electrospun fiber web and average diameter of fibers are almost the same as that of single nozzle electrospinning. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of thrust on supersonic gas jet penetration in gas-solid fluidized beds

Most of the jet penetration studies in gas-solid fluidized beds are for subsonic gas jets, for which many correlations can be found in the literature. In this work, horizontal supersonic gas jets, produced by convergent-divergent nozzles, have been studied, and the intent was to investigate the relationship between the thrust produced by supersonic nozzles and the jet penetration. Different nozzle geometries were used, with three gases having different characteristics (air, helium and carbon dioxide) and at different pressures. All the experimental runs were performed with silica sand particles with the same particle size distribution, and the fluidization velocity was set at a constant value of 0.09 m/s.Jet penetration was measured with a set of triboelectric probes, and it was found that the correlation proposed by Merry, although originally developed for subsonic gas jets, fits really well the experimental results. It was also confirmed that jet penetration displays a strong correlation with the thrust produced by the convergent-divergent nozzles.A correlation originally proposed by Benjelloun's has been modified and the corrected correlation gives the best predictions for gas jet penetration     

不同形状喷嘴的射流流动与卷吸特性

在不同雷诺数下,基于ANSYS Fluent 6.3软件对圆、椭圆、正方、十字、三角5种形状喷嘴的射流卷吸特性进行数值模拟,分析了轴向射流时均速度分布. 结果表明,三角形喷嘴的射流轴向最大时均速度最大,不同形状喷嘴的射流轴向最大时均速度均随轴向位置增大呈幂函数关系衰减;射流穿透深度与雷诺数和弗劳德准数存在多元线性关系;随轴向位置增大,射流横截面形状由初始段内喷嘴形状逐渐向圆形转化并最终扩展为圆形边界;射流轴线速度半值宽随轴向位置增加呈线性增大趋势,三角形喷嘴的卷吸率是十字形喷嘴的1.92~2.32倍.     

空气喷射技术的现状与发展

介绍了国内外空气喷射及喷嘴技术的现状、研究开发、应用领域及市场。重点分析了空气变形纱(ATY)、膨体纱(BCF)以及网络加工用喷嘴的技术更新。空气喷射技术主要应用于ATY,BCF,DTY的生产,节能降耗显著,建议国内建立行业空气喷射技术及专件研究中心,提高喷嘴的性能。     

油剂逆流接触提升管进料段固含率及颗粒速度的径向分布

在一套大型冷模实验装置中,考察了喷嘴射流与催化剂逆向接触的提升管进料段固含率和颗粒速度沿径向的分布及其对操作条件的影响,并与传统提升管进料段结构进行对比. 结果表明,沿轴向由下至上可将该新型结构的进料段分为喷嘴上游过渡区(H=-0.675~-0.375 m)、喷嘴射流控制区(H=-0.375~0.375 m)及喷嘴下游过渡区(H=0.375~0.675 m). 与传统形式相比,新型结构可使进料喷嘴安装截面以上射流影响区的高度明显缩短,喷嘴截面以下影响区域范围增大;油剂初始接触区域内催化剂沿径向的分布更均匀. 根据实验结果,得到新型进料段中射流控制区内典型截面固含率径向分布的经验模型,计算值与实验值吻合较好.     

Nozzles for equipment for semicontinuous casting of stainless steels under synthetic slag

Summary The most aggressive influence is exerted by synthetic slag on aluminosilicate refractories, and the least — on zirconia and graphite-containing refractories.During the casting of steel under synthetic slag, high-alumina, zircon, and zirconia nozzles were cracked in the first minutes of operation and did not insulate the jet of metal from slag.Alumina-graphite, alumina-silicon carbide and alumina-graphite nozzles during the casting of steel did not crack, were only slightly eroded with slag and metal and provided normal working of the continuous casting plant.Alumina-graphite or alumina-graphite elongated nozzles are recommended for a unit used for the semicontinuous casting of titanium-containing steels involving synthetic slag.     

FJCA16—4型煤用喷射式浮选机的循环量优化

介绍临涣选煤厂3台FJCA16—4型煤用喷射式浮选机在入料相同的工作条件下，对不同的工作压力、喷嘴出口直径分别进行成对对比的工业性试验，并根据数理统计的t检验方法，分别确定出合适的工作压力、喷嘴出口直径，从而获得最优的循环量。     

大型双射流流化床的流体动力学特性

在Ф0 .5m× 8m大型双射流流化床中 ,通过摄像、放像逐帧分析法和sthVCD软件分析录像转换的VCD ,得到了不同管间距下双射流典型的运动图像 .同时研究了两射流独立存在区、过渡区和射流合并区 3种流型的相互转变 ,得出了流型转变的关系式 .不同射流管间距下相同射流气速的射流深度相比 ,管间距减小则射流深度减小 ;在较小的管间距和相对高的射流气速下 ,两射流在射流深度之内始终合并 ,表现为射流合并高度 .得出了射流深度、射流合并高度的定量关系式 .分数维关联维数表明大型双射流流化床是一个确定性混沌系统 ,考查了管间距、静床高度对关联维数的影响     

超细气流粉碎基础理论的研究现状及发展

从颗粒在高速气流中的加速规律研究、颗粒冲击粉碎规律的研究、气流粉碎机的参数研究 3个方面综述了气流粉碎基础理论的发展状况 ,并指出了目前急需研究的一些问题。